The long range objective of the proposed research is to contribute to an understanding of the primary physico-chemical processes that link the photochemical transformation of visual pigment to the neural excitation of photoreceptor membranes. Specifically, we propose to study the molecular mechanism of early receptor potential (ERP) generation, and its relation to the primary photobiological events in the photoreceptor membranes. We propose to utilize various techniques of forming artificial model rhodopsin membranes and to apply a novel concept of chemical capacitance and a novel method of tunable voltage clamp (quasi-short-circuit) measurement to investigate the kinetic processes of the photoelectric effect in rhodopsin model membranes. In conjection with pulse laser light excitation, the tunable voltage clamp technique and the interpretation of experimental data in terms of chemical capacitance will allow us to probe the previously inaccessible region of a few angstrom near the membrane-water interface at a time resolution of 1 microsecond or better. This will provide direct electrokinetic information at the level of the photoreceptor membrane. Understanding of the molecular mechanism of ERP generation will make it possible to use the ERP as an indicator of the primary electrokinetic events occurring in the photoreceptor membranes.